The present invention relates to an image evaluation method and a charged particle beam device.
When performing a three-dimensional image reconstruction process that utilizes a focused ion beam scanning electron microscope (FIB-SEM), energy-dispersive X-ray spectrometry, wavelength-dispersive X-ray spectrometry, electron backscatter diffraction, or the like, it is necessary to continuously acquire an image using an electron microscope and store analysis result data for a long time.
In order to carry out above analysis, inspection and process, a technique which can maintain the electron beam irradiation area constant is necessary, because data is acquired for a long time and in particular a destructive inspection which utilizes an FIB-SEM must process the specimen without fail. One of the methods that corrects the electron beam irradiation position using a pattern matching process is known as a method for maintaining an electron beam irradiation area constant.
For example, JP-A-2008-270073 discloses a technique that reconstructs a three-dimensional image using an FIB-SEM, wherein a correction mark is formed in advance using a focused ion beam, and a pattern matching process is performed using the correction mark as a reference to correct the irradiation position.
More specifically, the correction mark is formed on the specimen using the FIB, the specimen is subjected to an FIB etching process to expose the cross section of the specimen, and then the exposed cross section is observed using the SEM so that the correction mark is included within the field of view to acquire a cross-sectional image. After performing the pattern matching process using the correction mark as a reference to correct the irradiation position, the specimen is subjected to the FIB etching process again to expose the cross section of the specimen, and the exposed cross section is observed using the SEM. This process is repeated to acquire a plurality of cross-sectional images for which the effect of drift is reduced. This makes it possible to accurately lay the plurality of cross-sectional images one on top of another to reconstruct a three-dimensional image.
The pattern matching process is performed by comparing a template image (that is part of an image (reference image) acquired in advance) and an image photographed under the same observation conditions (e.g., accelerating voltage and magnification) as those used for the reference image to determine the shift amount and the shift direction, for example.
Nevertheless, what kind of an image is appropriate for a template highly depends on the matching technique, and it is difficult to determine it unless a user is familiar and has lots of experience with matching technique. If the template is not appropriate, it is difficult to accurately perform the pattern matching process with respect to the comparative image and accurately determine the shift amount and the shift direction between the images.
Therefore, it is necessary to determine (evaluate) whether or not the template image is appropriate by continuously acquiring an image and performing the pattern matching process. In this case the user must always monitor whether or not the pattern matching process is accurately performed, and the device normally operates. This has imposed a significant burden on the user.
In view of above, an evaluation method has been desired that allows a user who is unfamiliar and does not have experience with the matching technique to determine (evaluate) whether or not the template image used for the pattern matching process is appropriate without continuously acquiring an image and performing the pattern matching process, for example.